Patterned liquid crystal alignment using ink-jet printed nanoparticles and use thereof to produce patterned, electro-optically addressable devices; ink-jet printable compositions

ABSTRACT

Ink-jet printable compositions including nanoparticles capped with a protective layer of hydrocarbon chains and a single solvent exhibiting a single evaporation rate and having a specifically defined viscosity and surface tension that result in uniform and printable alignment layers for liquid crystal materials. Patterned liquid crystal-containing cells are also disclosed including one or more layers including the same or different nanoparticles capped with a protective layer of hydrocarbon chains printed on a surface of a substrate or even another nanoparticle-containing layer. Methods for producing the cells are also disclosed, including the step of printing a pattern on one or more portions of a cell surface utilizing a composition comprising the capped nanoparticles. Devices including the cells are also disclosed.

FIELD OF THE INVENTION

This present invention relates to ink-jet printable compositionsincluding nanoparticles capped with a protective layer of hydrocarbonchains and a single solvent exhibiting a single evaporation rate andhaving a specifically defined viscosity and surface tension that resultin uniform and printable alignment layers for liquid crystal materials.

Patterned liquid crystal-containing cells are also disclosed includingone or more layers including the same or different nanoparticles cappedwith a protective layer of hydrocarbon chains printed on a surface of asubstrate or even another nanoparticle-containing layer, wherein the oneor more layers are printed with desirable resolution and precision, andwherein the capped nanoparticle-containing layer can be used to affectthe electro-optical response of the cell adjacent the area of the layer.

Methods for producing the cells are also disclosed, including the stepof printing a pattern on one or more portions of a cell surfaceutilizing a composition comprising the capped nanoparticles. In oneembodiment, the method includes the step of simultaneously printing twoor more different metal nanoparticle-containing ink compositions on asurface of a cell. An additional method includes the step of printing asecond layer of capped nanoparticle-containing ink on a firstnanoparticle-containing layer. Advantageously, thenanoparticle-containing inks can be printed on inflexible as well asflexible surfaces. Devices including the cells are also disclosed.

BACKGROUND OF THE INVENTION

Liquid crystals (LCs) have assumed their place as one of the mostimportant materials of the information age. LC displays (LCDs) play asignificant role in our everyday life; from handheld personal devices toprofessional applications and large-panel LCD TVs. LCs are liquidspossessing long-range orientational ordering, lacking in most instances(phases) long-range positional ordering of the constituent molecules. Inthe case of the one-dimensionally ordered fluid nematic phase used inmost display applications, intrinsic elastic interactions align the LCmolecules along some preferred direction (director), which in most casesforms the optical axis of the material. Typically, nematic LCs are usedin thin films, sandwiched between two glass substrates featuringtransparent electrodes (usually indium tin oxide, ITO). These substratesare covered with so-called alignment layers, whose main role is todefine the boundary conditions of the director to ensure uniformdistribution of the optical axis is the entire LC thin film. Thesepredominant boundary conditions are referred to as “homogeneous”(director lies in the plane of the thin film; usually with a smallpre-tilt), “homeotropic” (director is normal to the plane of the thinfilm) or, less frequently, intermediate “tilted”.

Alignment layers commonly feature some type of anisotropy that induces apreferred orientation for the LC director on the surface.Unidirectionally rubbed polyimides are the most widely used alignmentlayers, providing stable alignment of nematic and smectic LCs forvarious display modes. However, this method also has numerousdisadvantages, such as polymer debris resulting from the rubbing with avelvet cloth (using rubbing machines) and inhomogeneous, site-dependentcontrast ratios in the final display, which can only be avoided bycareful monitoring of the manufacturing conditions in clean rooms, seeJ. van Haaren, Nature 2001, 411, 29. Ion-beam deposition or plasmabombardment of thin polymer, SiN_(x), diamond-like carbon, or other thinfilms deposited on substrates are studied as well, see for example: (a)K. D. Harris, A. C. van Popta, J. C. Sit, D. J. Broer, M. J. Brett, Adv.Funct. Mater. 2008, 18, 2147; (b) Y. H. Kim, H. G. Park, B. Y. Oh, B. Y.Kim, K. K. Paek, D. S. Seo, J. Electrochem. Soc. 2008, 155, J371; (c) G.Hegde, O. Yaroshchuk, R. Kravchuk, A. Murauski, V. Chigrinov, H. S.Kwok, J. Soc. Inf. Display 2008, 16, 1075., and of these techniques, theglancing angle ion beam bombardment of diamond-like carbon used for themanufacturing of smaller LCD panels by IBM, see P. Chaudhari, J. Lacey,J. Doyle, E. Galligan, S. C. A. Lien, A. Callegari, G. Hougham, N. D.Lang, P. S. Andry, R. John, K. H. Yang, M. H. Lu, C. Cai, J. Speidell,S. Purushothaman, J. Ritsko, M. Samant, J. Stohr, Y. Nakagawa, Y. Katoh,Y. Saitoh, K. Sakai, H. Satoh, S. Odahara, H. Nakano, J. Nakagaki, Y.Shiota, Nature 2001, 411, 56.

Photoalignment and obliquely evaporated inorganic materials arealternative techniques that are utilized as well, for a recent review,see: O. Yaroshchuk, Y. Reznikov, J. Mater. Chem. 2012, 22, 286; for areview summarizing work up to 2000: K. Ichimura, Chem. Rev. 2000, 100,1847; for representative examples, see: (a) J. Hoogboom, M. Behdani, J.A. A. W. Elemans, M. A. C. Devillers, R. de Gelder, A. E. Rowan, T.Rasing, R. J. M. Nolte, Angew. Chem., Int. Ed. 2003, 42, 1812; (b) J.Hoogboom, P. M. L. Garcia, M. B. J. Otten, J. A. A. W. Elemans, J. Sly,S. V. Lazarenko, T. Rasing, A. E. Rowan, R. J. M. Nolte, J. Am. Chem.Soc. 2005, 127, 11047; (c) Y. Morikawa, S. Nagano, K. Watanabe, K.Kamata, T. Iyoda, T. Seki, Adv. Mater. 2006, 18, 883; (d) O. Klikovska,L. M. Goldenberg, J. Stumpe, Chem. Mater. 2007, 19, 3343; (e) L. O.Vretik, V. G. Syromyatnikov, V. V. Zagniy, E. A. Savchuk, O. V.Yaroshchuk, Mol. Cryst. Liq. Cryst. 2008, 486, 1099; (f) C. Kim, J. U.Wallace, S. H. Chen, Macromolecules 2008, 41, 3075; (g) Y. Yi, M. J.Farrow, E. Korblova, D. M. Walba, T. E. Furtak, Langmuir 2009, 25, 997;(h) S. Droge, M. O'Neill, A. Lobbert, S. P. Kitney, S. M. Kelly, P. Wei,D. W. Dong, J. Mater. Chem. 2009, 19, 274; J. L. Janning, Appl. Phys.Lett. 1972, 21, 173. Although these processes have demonstrated theirdurability and have been implemented in large-scale productionenvironments, they usually require many fabrication steps, highprocessing temperatures, and sometimes, high vacuum environment.

In addition, many LC applications require patterned alignment of the LCto provide spatial modulation of the optical axis, for example, for thewave front control applications. Usually, in order to obtain patternedalignment, complicated and expensive photolithography techniques must beused. With the use of photoalignment, the process can be significantlysimplified, but still requires design and fabrication of photo-masks aswell as the deposition of a photosensitive polymer layer using spincoating and baking. Other approaches include micropatterning using asharp stylus, see G. P. Sinha, C. Rosenblatt, L. V. Mirantsev, Phys.Rev. E 2002, 65, 041718; (b) J. H. Kim, M. Yoneya, H. Yokoyama, Nature2002, 420, 159, or micro-rubbing (μ-rubbing) of polyimides S. Varghese,S. Narayanankutty, C. W. M. Bastiaansen, G. P. Crawford, D. J. Broer,Adv. Mater. 2004, 18, 1600.

Another promising technique refined by Abbott and co-workers makes useof alkylthiol self-assembled monolayers (SAMs), see O. Guzman, N. L.Abbott, J. J. de Pablo, J. Chem. Phys. 2005, 122, 184711; (b) G. M.Koenig, M. V. Meli, J. S. Park, J. J. de Pablo, N. L. Abbott, Chem.Mater. 2007, 19, 1053; (c) V. K. Gupta, W. J. Miller, C. L. Pike, N. L.Abbott, Chem. Mater. 1996, 8, 1366; (d) R. A. Drawhorn, N. L. Abbott, J.Phys. Chem. 1995, 99, 16511, either on thin gold films sputtered onglass or gold islands immobilized on surfaces via electron beamevaporation, which, depending on the chain length, combination of chainlengths, and functionalization, can induce multiple alignment scenariosin nematic LCs, see (a) H. T. A. Wilderbeek, F. J. A. van der Meer, K.Feldman, D. J. Broer, C. M. W. Bastiaansen, Adv. Mater. 2002, 14, 655;(b) H. T. A. Wilderbeek, J. P. Teunissen, C. W. M. Bastiaansen, D. J.Broer, Adv. Mater. 2003, 15, 985. Photopatterning, S. D. Evans, H.Allinson, N. Boden, T. M. Flynn, J. R. Henderson, J. Phys. Chem. B 1997,101, 2143, or microcontact printing (μCP) using SAMs pioneered byWhitesides, A. Kumar, G. M. Whitesides, Appl. Phys. Lett. 1993, 63,2002, also allow for patterned alignment of nematic LCs, but stillrequire multiple fabrication steps such as etching of a silicon wafermaster to prepare PDMS stamps (that can be used many times for the samepattern, but not altered), see (a) J. P. Bramble, S. D. Evans, J. R.Henderson, C. Anquetil, D. J. Cleaver, N. J. Smith, Liq. Cryst. 2007,34, 1059; (b) C. Anquetil-Deck, D. Cleaver, Phys. Rev. E 2010, 82,031907.

In most cases, simple processes with fewer steps lead to lowerproduction costs and higher yields. The development of simpler processesfor the patterned alignment of LCs would facilitate the development oflow-cost electro-optical devices such as adaptive LC-based lenses, seeL. Li, L. Shi, D. Bryant, T. van Heugten, D. Duston, P. J. Bos, Proc.SPIE Optoelectronic Interconnects and Component integration XI 2011,7944, 79440S, or adaptive Bragg diffraction gratings, see C. C. Bowley,P. A. Kossyrev, G. P. Crawford, S. Faris, Appl. Phys. Lett. 2001, 79, 9.

The effect of homeotropic alignment of nematic LCs via doping with asmall quantity of thiol-capped gold nanoparticles (NPs) has recentlybeen demonstrated, see H. Qi, B. Kinkead, T. Hegmann, Adv. Funct. Mater.2008, 18, 212; H. Qi, T. Hegmann, ACS Appl. Mater. Interf. 2009, 1,1731; and M. Urbanski, B. Kinkead, H. Qi, T. Hegmann, H.-S. Kitzerow,Nanoscale 2010, 2, 1118. The NPs migrate and adsorb to the interfaceformed between the LC films and the substrate, where they inducehomeotropic alignment of the director over the entire area of the cell.A similar effect is achieved if NPs are deposited onto the surfacebefore filling of the test cell with the LC material. This leads to auniform coverage of the surface with the NPs and, in turn, uniformvertical alignment of the LC over the entire area. The homeotropicanchoring of the LC molecules on the NPs is accompanied by a contrastinversion effect, i.e. under the action of a low-frequency electricfield, “dielectrically positive” LCs (Δϵ>0, the dielectric anisotropy Δϵis defined as Δϵ=ϵ_(∥)−ϵ_(⊥), where ϵ_(∥) is the dielectric permittivityparallel to the long molecular axis and ϵ_(⊥) the dielectricpermittivity perpendicular to the long molecular axis) effectively actas dielectrically negative nematic LC (Δϵ<0) and undergoes a transitionfrom the homeotropic to the homogenous state, see H. Qi, B. Kinkead, T.Hegmann, Adv. Funct. Mater. 2008, 18, 212. This dual-alignmentcapability can form the basis for numerous useful applications.

SUMMARY OF THE INVENTION

In view of the above, a problem of the present invention was to providehigh precision control of nanoparticle-induced liquid crystal alignment.The indicated problem is solved by the methods of the present inventionwhich allow patterned alignment of liquid crystals, preferably nematicliquid crystals in one embodiment, which provides a quick, simple, andhighly versatile and adaptable liquid crystal alignment technique.

Accordingly, it is an object of the present invention to providepatterned structures with modulated director configuration in the liquidcrystal cells utilizing ink-jet printing of a composition comprisingnanoparticles or nanomaterials capped with a protective layer ofhydrocarbon chains (NPs), wherein the fabricated structures and patternscan be used for nanomaterial-based electronics, see for example S.Volkman, Y. Pei, D. Redinger, S. Yin, V. Subramanian, Mater. Res. Soc.Symp. Proc. 2004, 814, 1781 and G. C. Jensen, C. E. Krause, G. A.Sotzing, J. F. Rusling, Phys. Chem. Chem. Phys. 2011, 13, 4888,biomaterials, see J. T. Delaney, J. P. Smith Jr., U. S. Schubert, SoftMatter 2009, 5, 4866, and liquid crystal displays, see V. J. Alino, K.X. Tay, S. A. Khan, K.-L. Yang, Langmuir 2012, 28, 14540. Striking andadvantageous features of the ink-jet printing process are thevariability of the NPs (metal, metal chalcogenide, carbon-based, etc.),wide choice of substrates and patterns as well as the scalability andsimplicity of the process.

Still another object of the present invention is to provideelectro-optical liquid crystal-containing devices, some havingrelatively low cost, such as, but not limited to adapted liquid crystalFresnel lenses, Bragg diffraction gratings, LCDs working in the verticalalignment mode with a patterned pixel design, flexible LCD and liquidcrystal sensors.

Yet another object of the present invention is to provide an ink-jetprintable composition, comprising a nanoparticle capped with aprotective layer of hydrocarbon chains, wherein the nanoparticlecomprises a metallic, metal oxide, metal chalcogenide, or carbon-basedcore; and a single solvent component having a defined viscosity andsurface tension that provides a single evaporation rate and results in auniform and printable alignment layer. In one embodiment the solvent hasa viscosity of 7 to 15 cPs and a surface tension of from about 20 toabout 50 dynes/cm. 0-xylene is one example of a suitable solvent.

Still another object of the present invention is to provide a liquidcrystal device having one or more same or different cappednanoparticle-containing layers printed on a surface of a substrate oreven another capped nanoparticle-containing layer, wherein the one ormore layers can be printed with desirable resolution and precision.

Accordingly, one aspect of the invention is an ink-jet printablecomposition, comprising a nanoparticle capped with a protective layer ofhydrocarbon chains; and a single solvent having a viscosity of about 7to about 15 cPs and a surface tension of about 20 to about 50 dynes/cm.

In another aspect of the invention, a method for forming a liquidcrystal cell is disclosed, comprising the steps of obtaining a cappednanoparticle-containing composition comprising a) a nanoparticle cappedwith a protective layer of hydrocarbon chains and b) a solvent; andprinting a first layer of the composition on one or more portions of acell surface with an ink-jet printer.

In a further aspect of the invention, a printed, patterned liquidcrystal device is disclosed, comprising at least two substantiallytransparent substrates; a substantially transparent conductive electrodelayer operatively connected to each substrate; optionally an alignmentlayer located on at least one of the conductive electrode layers; aprinted layer located on a portion of one or more of the electrode layerand the alignment layer, and the printed layer derived from acomposition comprising a nanoparticle capped with a protective layer ofhydrocarbon chain and a solvent, wherein an electro-active liquidcrystal material is present between the at least two substantiallytransparent substrates and is in contact at least the printed layer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows (a) schematic image of the substrate design of an LC cellwith ITO electrodes and alignment layers (continuous layer of 30°SiO_(x) and multiple, separate, patterned printed layers of gold NPs);(b) schematic image of the hybrid structure of the cell with NPs printedon one of the surfaces featuring a homogeneous alignment layer (bottom),and a second surface with a homeotropic alignment layer (NP inducedhomeotropic—hybrid patterning), wherein the rubbing direction or easyaxis of orientation of the SiO_(x) alignment “underlayer” determine thedirection of planar alignment in the non-printed domains in (a) and (b);(c) spherical pixels (droplets) printed using gold NPs (bright fieldmicrograph), and (d) possible alignment/electro-optic pattern(homeotropic pixels in planar cell and vice versa using applied electricfields);

FIG. 2 shows LC textures and alignment patterns in cells (cell gap: 5μm) created by printed NPs in the polarized light microscope (crossedpolarizers): (a) MLC-6610 on bare ITO (top and bottom substrate); (b)MLC-6610 on the rubbed polyimide PI-2555—homogeneous alignment; (c)MLC-6610 on rubbed polyimide PI-2555—distorted (tilted) alignment; (d)5CB on rubbed polyvinyl alcohol, wherein in all cells, two identicalsurface alignment layers are used, and the NPs are only printed on onlyportions of one of the substrates;

FIG. 3 shows LC texture and alignment patterns of MLC-6610 in cells(cell gap: 5 μm) with the NPs printed on the surface of 30° SiO_(x)observed in polarized light optical microscope (crossed polarizers): (a)alpha-numerical pattern; (b) alphanumerical pattern (entire cell); (c)linear pattern; (d) large-feature, square pattern, wherein the oppositesurface of these cells is covered with rubbed homeotropic polyimideSE-1211;

FIG. 4 shows Electro-optic response of the LC cells under an applied DCelectric field; LC material: Felix-2900-03; NPs printed on the varioussurfaces: (a) Substrate 1: ITO+30° SiO_(x)+printed NPs, Substrate 2:ITO+PI-1211 substrate; (b) two ITO+30° SiO_(x)+printed NPs substrates;(c) Substrate 1: ITO+30° SiO_(x)+printed NPs, Substrate 2:ITO+PI-1211+printed NPs;

FIG. 5 shows (a) Hybrid cell filled with 5CB (bottom substrate: rubbedpolyimide PI-2555+printed NPs on glass, top substrate: ITO on glass)showing NP printed domain with different pre-tilt (red arrow showsrubbing direction of PI-2555 substrate); (b) a 6 by 7 array of cells ona 7×7 inch glass wafer with square printed NP alignment patterns; (c)magnified section of the letter “C” printed with NPs on an ITO-coatedglass substrate cell (top and bottom) showing the quality of thehomeotropic alignment (contrast) and the sharp boundary to thehomogeneous aligned domains (LC: TL203);

FIG. 6 shows UV-vis spectrum of the dodecanethiolate-capped Au NPs;

FIG. 7 shows TEM micrographs of the dodecanethiolate-capped Au NPs.Average NP size: 1.9±0.4 nm (from TEM image analysis using ImageJ ofmore than 100 particles);

FIG. 8 shows TGA thermogram of the dodecanethiolate-capped Au NPsshowing an onset of weight loss at 140° C. as reported by Joseph et al.using XPS analysis;

FIG. 9 shows ¹H NMR spectrum of dodecanethiolate-capped Au NPs (δ[ppm]:1.29 (CH₂), 0.93 (CH₃) with characteristic peak broadening;

FIG. 10 shows jetting waveform used for the ink-jet printing of thenano-ink;

FIG. 11 shows “drop-watcher” of Dimatrix printer (multi-nozzle-mode)using gold NP ink;

FIG. 12 shows FIB-SEM images of the printed multi-layer of Au NPs. Thetwo images presented are different regions on the substrate and aretaken with magnifications of 25,000× (top) and 50,000× (bottom). Theaveraged thickness of the NP multi-layer was calculated to be ˜28 nm,i.e. about 5 layers of densely packed Au NPs;

FIG. 13 shows determining the polar anchoring energy using the slopefitting method following. The result of W=6.8×10⁻⁴ J/m² was obtained forthe 4.8 μm MLC6610 VA cell with the printed NPs used as the homeotropicalignment layer;

FIG. 14 shows square alignment pattern (fully homeotropic) for variousnematic LCs (Surface 1: ITO+30° SiO_(x)+printed NPs; Surface 2: ITO+30°SiO_(x)+printed NPs): (a) Felix-2900-03 (printed pattern at right), (b)MLC-6610 (printed pattern at top), and (c) TL203 (printed pattern topleft);

FIG. 15 shows dual electro-optic mode for Felix-2900-03 observed oncooling from the isotropic phase 3° C. below T_(Iso/N) in a cell withthe following substrates (left side with printed square feature):surface 1: ITO+30° SiO_(x)+printed NPs; surface 2: ITO+30°SiO_(x)+printed NPs. (a) E=0 V, (b) Field ON: E=5 V DC, (c) Field OFF:E=0 V, (d) Field ON: E=−5 V, and (e) Field OFF: E=0 V. (DC or lowfrequency AC field, 0.5 Hz); and

FIG. 16 shows dual electro-optic mode observed for Δϵ<0 LC mixtureMLC-6610 at room temperature in a cell (cell gap: 5 μm) with thefollowing substrates: surface 1: ITO+printed NPs with L-shaped feature(width: 200-300 μm; surface 2: ITO. DC and AC (0.5 Hz-1 kHz) voltages asindicated in the figure.

DETAILED DESCRIPTION OF THE INVENTION

As described herein above, ink-jet printing of compositions includingcapped nanoparticles having a protective layer of hydrocarbon chains anda solvent is disclosed as a versatile and highly efficient means topattern the alignment of liquid crystals, preferably nematic liquidcrystals in one embodiment. Any homeotropic alignment patterns can becreated quickly, for example ranging in size from 30 micron (850 dpi) toseveral inches², with high accuracy that does not deteriorate with time.Depending upon the alignment underlayer, intermediate configurationsbetween homeotropic and homeogeneous are also producible. In oneembodiment nematic liquid crystals with both positive and negativedielectric anisotropy can be switched by applying a DC or AC electricfield in the printed vertical domains with the substrate configurationdetermining the electro-optic response.

Many liquid crystal-based electro-optical devices such as diffractiongratings, Fresnel zone plates, adaptive lenses, or sensors requirepatterned alignment surfaces. Typically such devices are fabricatedusing complicated techniques such as photolithography orphoto-alignment. While these methods provide good resolutions andpredictable results, they are time consuming, and the patterningsurfaces do not actively influence the electro-optical response of theliquid crystal. In addition, there are limitations regarding the typesof substrates that can be used.

Printable Ink Compositions

The ink-jet printable compositions of the present invention have toconform to the requirements of Piezo-based nozzles of the printercartridges requiring specific viscosities and surface tension. Forexample, in one embodiment the compositions include a single solventthat provides a viscosity in a range generally of about 7 to about 15cPs and preferably from about 10 to about 12 cPs. The solvent has asurface tension in a range generally from about 20 to about 50 dynes/cmand preferably from about 28 to about 42 dynes/cm.

The capped nanoparticles should not aggregate substantially in thecomposition and the carrier fluid or solvent should have a boiling pointunder mild vacuum lower than 100° C. as well as sufficiently high vaporpressure to allow evaporation of the solvent without any substantialdecomposition of the nanoparticles. Thus, it should be clear that afterprinting the ink-jet-printable compositions of the present invention,the printed layer derived from the composition comprising the cappednanoparticle and solvent is free of or substantially free of the solventdue to solvent evaporation.

In view of the above, in one embodiment the solvent is o-xylene.Multi-solvent systems induce aggregation of the nanoparticles on theprinted substrate during solvent evaporation, since one solvent usuallydisplays a higher vapor pressure (or boiling point). Additionally,aggregation is seen because the nanoparticles show a differentsolubility in the solvents making up the multi-solvent carrier fluid.

When deposited or fixed on a cell substrate, for example an electrodelayer or alignment layer, the deposited nanoparticles capped with aprotective layer of hydrocarbon chains are used to affect the alignmentof the liquid crystal of the cell adjacent to the deposited cappednanoparticle-containing layer. Suitable nanoparticles include, orcomprise a metallic, metal oxide, metal chalcogenide, or carbon-basedcore. In one embodiment, an ink-jet printable composition and layersand/or layer printed therewith comprises one or more of a nanoparticlecomprising a metallic core, a nanoparticle containing a metal oxidecore, a nanoparticle containing a metal chalcogenide core and ananoparticle containing a carbon-based core.

The metal of the metal core-containing nanoparticle may be, for example,gold, silver, platinum, or palladium. In a preferred embodiment, themetal is gold. Functionality is provided to the metal core-containingnanoparticles by bonding functional groups to the metal.

A functional group may be bonded to the metal through any one of avariety of linkages, for example, the chiral group may be any grouphaving one or more chiral centers. For example, the chiral group may bea chiral ester such as 6-sulfanylhexyl(2S)-(6-methoxy-2-naphthyl)propanoate, 12-sulfanyldodecyl(2S)-(6-methoxy-2-naphthyl)propanoate, (2S)-methylbutyl7-sulfanylheptanoate, or an enantiomer thereof or any other chiraldopant structure known to induce a chiral nematic liquid crystal phase.Various metal core-containing nanoparticles are described for example inU.S. Pat. Nos. 8,071,181 and 8,294,838 and herein incorporated byreference.

The nanoparticles comprising a metal chalcogenide core that are utilizedin some embodiments to form a ink-jet printable composition and aprinted layer include semiconductor quantum dots or rods. A “quantumdot” is a semiconductor nanoparticle that can confine the motion ofelectrode or holes in all three spatial directions. A “quantum rod” or“nanorod” is a semiconductor nanoparticle in the form of a rod. Quantumdots and rods may be made by, for example, colloidal synthesis,electrochemical techniques, or pyrolytic synthesis. “Nanocluster” and“nanoparticle”, as used herein, are synonymous and include, but are notlimited to, quantum dots (e.g. CdTe and CdSe quantum dots and quantumrods). Various nanoparticles comprising a metal chalcogenide core aredisclosed in U.S. Pat. No. 8,323,755, herein incorporated by reference.

The carbon-based nanoparticles that are utilized in some embodiments ofink-jet printable compositions and layers printed therewith include, butare not limited to, carbon dots, graphene dots, and carbon nanotubes.

The average size, herein the largest dimension of a capped nanoparticle,for example a diameter of a sphere, is no greater than 10 or 25nanometers (nm). In one embodiment the capped nanoparticle average sizeranges from about 1 to about 10 or 25 nm. In other embodiments, theaverage size is from 1 to 9 nm, 1 to 8 nm, 1 to 7 nm, 1 to 6 nm, 1 to 5nm, 1 to 4 nm, 1 to 3 nm, or 1 to 2 nm. Unless otherwise noted herein,the average size of the capped nanoparticles provided is the averagesize of the core, for example a gold core, silver core, or CdTe core, ofthe capped nanoparticle, wherein the measurement of size does notinclude the functionality attached to the core. The average size of thenanoparticle can be measured using techniques that utilize, for example,x-ray scattering and/or transmission electron microscopy.

The capped nanoparticles of the printable composition are present in anamount that does not substantially affect the viscosity of the solventon one hand and also to provide for desired alignment characteristics onthe other hand. That said, the concentration of the capped nanoparticlesin the solvent ranges generally from about 10 to about 100 mg/ml,desirably from about 10 to about 75 mg/ml, and preferably from about 15to about 50 mg/ml. In one embodiment the capped nanoparticles arepresent in a concentration that provides at least a monolayer surfacecoverage on a desired surface of the cell to which the printablecomposition is applied.

The printable composition is formed in one embodiment by combining thecomponents to form a solution, generally by mixing or dispersing thenanoparticles capped with a protective layer of hydrocarbon chain in thesolvent. In one embodiment the solution is sonicated, for example in anultrasonic water bath for a suitable period of time, for example oneminute, before filling a printing cartridge therewith.

Patterned Liquid Crystal Cells and Devices

The liquid crystal cells of the present invention include a pair ofsubstrates, see FIG. 1(b) for example. In one embodiment, the pair ofsubstrates is substantially planar and disposed substantially parallelto each other. The substrates are maintained at a desired distance byspacers in various embodiments. The spacing range can vary, and in oneembodiment ranges from about 1 to about 15 microns, desirably from about3 to about 10 microns, and preferably from about 4 to about 7 microns.An electrode layer is present on each inner surface of the cellsubstrates. In some embodiments, one or more patterned electrode layersare utilized.

If desired, an alignment layer is present on one or more portions of anelectrode layer. In one embodiment an alignment layer is present on anelectrode layer of one cell substrate. In a further embodiment, analignment layer is present on each electrode layer of each cellsubstrate.

The printed, capped nanoparticle-containing composition layer is presenton one or more portions of a cell surface. For example, the printedlayer can be printed directly on the electrode layer or an alignmentlayer when present, or both, depending upon the cell construction. Insome embodiments each of a portion of an alignment layer and a printedcapped nanoparticle-containing composition layer are in contact with anelectrode layer. As noted herein, in view of the ability of the cappednanoparticle-containing printable composition to be applied to thedesired cell surface with high precision, precise patterns can beformed. In addition, a plurality of different printable compositionseach containing a different type of nanoparticle can be applied to acell surface, resulting in multiple patterns comprising differentnanoparticles.

Furthermore, in various embodiments, a second layer of a printablecapped nanoparticle-containing composition containing a same ordifferent nanoparticle can be printed over a first layer printed on acell surface. Multiple stacked layers of a printed, cappednanoparticle-containing composition can be utilized to affect thealignment of the liquid crystal mixture utilized in the cell. Thus, onecan tune the pre-tilt angle of the liquid crystal. In some embodiments,the pre-tilt of the liquid crystal can be overridden by printingmultiple layers of the printable nanoparticle-containing compositionover one another. In various embodiments, the printed composition can bepresent on a portion of each substrate, for example one or more of anelectrode layer and/or alignment layer of a lower substrate and one ormore of an electrode layer and/or alignment layer of an upper substrate.

As various printers have two or more different ink-jet nozzles, two ormore different nanoparticle-containing printable compositions can beprinted simultaneously which allows for rapid cell construction.

A liquid crystal layer is present between the substrates and in contactwith at least the printed capped nanoparticle-containing composition andfurther an alignment layer when present and not covered by a printedlayer. As utilized herein, the term “layer” does not require a uniformthickness, and imperfections or uneven thicknesses can be present solong as the layer performs its intended purpose.

The substrates utilized in the present invention must provide desiredoptical transmission and preferably are transparent. The substrates canbe planer or curved. Furthermore, in some embodiments the substrates areflexible. Various materials can be utilized as known in the art, suchas, but not limited to, glass, quartz, or a polymer. Glass is preferredin an embodiment where flexibility is not required. In some embodiments,the substrate is a non-birefringent material, or aligned and compensatedto minimalize the effect of the birefringence.

The conductive electrode layer can be deposited on a substrate by anyknown method. The electrode layer material can be any inorganic,substantially transparent conductive material. Examples of suitablematerials include, but are not limited to, a metal oxide such as indiumoxide, tin oxide, and indium tin oxide, and preferably are indium tinoxide in one embodiment. The electrode layer must be sufficiently thickto provide desired conductivity. That said, the thickness of theconductive electrode layer ranges generally from about 5 to about 250nm.

When present, the alignment layer is used to induce a particulardirectional orientation in the liquid crystal when no voltage is appliedto the cell. Various materials suitable for use as alignment layers areknown in the art. For example, alignment layers include, but are notlimited to, polyimide, polyvinyl alcohol, and 30° SiO_(x). The thicknessof the alignment layer should be sufficient to impart the desireddirectional orientation to the liquid crystal material. In someembodiments, the alignment layer has a thickness that ranges generallyfrom about 50 to about 500 nm. In some embodiments, the alignment layercan be treated by rubbing to impart a substantially homogeneousmolecular orientation to the liquid crystal material prior to anelectric field being applied to the cell.

Generally any liquid crystal material that has an orientational orderthat can be controlled in the presence of an electric field can beutilized. In various embodiments, nematic, smectic, or cholesteric phaseforming liquid crystals or polymer-containing liquid crystals such aspolymer liquid crystals, polymer dispersed liquid crystals, or polymerstabilized liquid crystals can be utilized. Nematic liquid crystals arepreferred in one embodiment. The nematic liquid crystals may havepositive dielectric anisotropy, Δϵ>0 or negative dielectric anisotropy,Δϵ<0. Non-limiting examples of suitable nematic liquid crystals include,but are not limited to, cyanobiphenyl derivatives such asFelix-2900-3,4′-n-pentyl-4-cyanobiphenyl (5CB),4′-n-octyl-4-cyanobiphenyl (8CB), or 4′-n-octyloxy-4-cyanobiphenyl(80CB).

While the homeotropic anchoring of the LC molecules on the NPs definesthe director orientation in the vicinity of the NPs, in the “blank”areas (non-printed) of the cell without NPs, the director orientationdepends on the exposed surface of the substrate. Hence, to achievecontrolled director configuration over the entire thin LC film, oneneeds to define the boundary conditions for the director everywhere,including the blank (non-patterned) areas. The simplest solution wouldbe to first deposit an alignment layer on the desired portions or areasof the electrode layer and then print the NPs directly atop, ensuringthat the alignment layer underneath the particles does not disrupt thehomeotropic alignment induced by the NPs themselves. To create themaximum amplitude of the optical axis modulation in the cell, thealignment “under-layer” needs to provide homogeneous alignment of theLC.

As the “under-layer”, we tested the performance of several standardalignment layer materials with varying polar anchoring energies such aspolyimide PI-2555 (anchoring energy ˜1 mJ/m², see M. Feller, W. Chen, Y.Shen, Phys. Rev. A 1991, 43, 6778.1), polyvinyl alcohol (anchoringenergy ˜10⁻¹ mJ/m², see Y. Cui, R. S. Zola, Y.-C. Yang, D.-K. Yang, J.Appl. Phys. 2012, 111, 063520), and SiO_(x) films evaporated at 30° withrespect to the evaporation direction, which provides zero pre-tiltalignment with the low anchoring energy of ˜10⁻² mJ/m², see G. Durand,Liq. Cryst. 1993, 14, 159.

The homogeneous alignment layers of PI-2555 and PVA were deposited usingthe standard process (spin-coating of the solution, evaporating of thesolvent, and baking). The 30° SiO_(x) was deposited onto the pre-cleanedITO-covered glass substrates. The quality of homogeneous alignment wastested by assembling a test cell made of two alignment layer surfacesand filling it with one of the used LCs, here Felix-2900-03 (for phasetransition temperatures and other properties of all LCs used and tested,see Table 1). The proposed design of the substrate of the LC cell isshown in FIG. 1a .

TABLE 1 List and properties of used LCs and LC mixtures. Transitiontemperatures/° C. LC Phase sequence EO Properties Felix-2900-03 Cr 52(SmA 45) N 70 Iso Δε = +0.62 (at T/T_(Iso/N) = 0.95) 5CB Cr 25 N 35 IsoΔε = +14.2, Δn = 0.1973 MLC-6610 T_(Iso/N) = 79 Δε = −3.1, Δn = ~0.07TL203 T_(Iso/N) = 74.6 Δε = +11.0, Δn = 0.2013

To define the director across the entire cell, the boundary conditionsmust also be set at the other surface. One possibility is assembling aLC cell using two identical substrates with printed NPs. In this case,an additional step of aligning the patterns on the two substrates isneeded. To eliminate this additional step, using a solid homeotropicalignment layer on the second substrate would lead to homeotropicdirector configuration over the printed areas and a hybrid configurationover the non-printed areas (FIG. 1b ). Although such configuration doesnot lead to the maximum possible amplitude of the optical axisdirection, this approach provides the simplest production process withthe elimination of the afore-mentioned pattern alignment step. It isimportant to induce a small pre-tilt to the homeotropic alignment layerto avoid director configuration degeneracy and prevent domains of thedifferent molecular orientation from forming in the cell. To realizethis, an alignment layer such as the homeotropic polyimide alignmentlayer SE-1211 was deposited on pre-cleaned ITO-coated glass substratesfor the second (top) substrate intended to be used for the hybrid cells.A solution of SE-1211 (Solvent type 26 from Nissan Chemicals,concentration 1:2) was spin-coated at 5000 rpm for 30 seconds, pre-bakedat 80° C. for 5 minutes, and baked at 210° C. for 45 minutes. Afterbaking, the substrates were unidirectionally rubbed to induce a pre-tiltof ˜5° with respect to the cell's plane normal (and the quality of thehomeotropic alignment was checked by assembling a test cell made of twosuch substrates covered with SE-1211 and again observing the alignmentof Felix-2900-03).

To demonstrate the versatility of this approach, we also printed NPs onbare ITO surfaces to show that patterned NP-induced LC alignment withoutthe use of any alignment “under-layer” can be realized as well. In thiscase, the NPs were only printed either only on one or both of thesurfaces.

The size of the printed droplet (“pixel” size) depends on the volume ofthe droplet (defined by the cartridge, for most experiments we used 10pL) and the substrate. In the case of SiO_(x), the resulting dropletsize is around 75 μm (˜340 dpi resolution), see The droplet or pixelsize depends on the wettability of the substrate, e.g., 75 μm on SiO_(x)vs. 70 μm on pre-cleaned glass, respectively, for a 10 pL droplet. Usinga cartridge with a droplet volume of 1 pL results in the pixel sizearound 30 μm (˜850 dpi resolution) as shown in FIG. 1c , but sincealignment and unique electro-optic response (FIG. 1d ), see H. Qi, B.Kinkead, T. Hegmann, Adv. Funct. Mater. 2008, 18, 212 and M. Urbanski,B. Kinkead, H. Qi, T. Hegmann, H.-S. Kitzerow, Nanoscale 2010, 2, 1118,are independent of pixel size we will discuss the results for the 10 pLcartridges. To achieve homogeneous features (pixels) we made use of theprecision overprinting feature of the printer, where the same patterncan be precisely printed a second time over an existing pattern (i.e.about four to six layers of NPs). Using this approach, the designedprinted patterns had the droplet spacing of 75 μm corresponding to thepixel size. Various printing patterns were designed using bitmap graphiceditor and imported as 1-bit bitmap files into the printer software. Theone-nozzle printing mode was used for the slower but more consistentprinting, but multi-nozzle printing could be used as well as notedherein. After printing, the substrates were placed in the vacuum ovenfor several hours at 35-40° C. to ensure complete evaporation of thesolvent (o-xylene). The thickness of dried printed layer was determinedby FIB-SEM.

From the SEM image (Figure S7), the average thickness of the dual layeroverprinted NP pixel was determined to be ˜28 nm (see experimentalsection for more details). This was found to be in excellent agreementwith theoretical estimations, which gave the layer thickness of 29.5 nmfor the double layer (for a printed droplet 70 μm in diameter). Thevarious cells were assembled with either only one or both substratesfeaturing printed NP patterns. Spherical silica spacers sprayed over oneof the substrates controlled the cell gap to 5±0.2 μm. The cells werefilled with the LC using the vacuum chamber (because the capillarymethod for the 5 μm gap sometimes led to the appearance of air bubblesin the cell). The printed patterns were stable under these fillingconditions and did not smear out.

The quality of LC alignment in the test cells with printed NPs on thevarious surfaces was visually assessed using polarized light opticalmicroscopy in the nematic phase of the LC. For Felix-2900-03, theobservation temperature was typically a few degrees below thenematic-isotropic transition temperature (˜70° C.), for theroom-temperature nematic LCs (5CB, MLC-6610, and TL203), all experimentswere performed at room temperature.

To characterize the aligning properties of the NPs, we measured thepolar anchoring energy using Yokoyama-van Sprang method, see H.Yokoyama, H. A. van Sprang, J. Appl. Phys. 1985, 57, 4520, enhanced byLavrentovich and co-workers, see Y. Nastishin, R. Polak, S.Shiyanovskii, V. Bodnar, and O. Lavrentovich J. Appl. Phys. 1999, 86,4199, and expanded to the homeotropic case by Wu et al., see X. Nie, Y.H. Lin, T. X. Wu, H. Wang, Z. Ge, S. T. Wu, J. Appl. Phys. 2005, 98,013516, which is based on the measurement of optical phase retardationas a function of applied voltage. We obtained a value of 6.8×10⁻⁴ J/m²(Figure S8, SI), which is, remarkably, of the same order of magnitude asreported for some commercially available nematic LC mixtures onhomeotropic polyimide alignment layers, see Y. Nastishin, R. Polak, S.Shiyanovskii, V. Bodnar, and O. Lavrentovich J. Appl. Phys. 1999, 86,4199 and X. Nie, Y. H. Lin, T. X. Wu, H. Wang, Z. Ge, S. T. Wu, J. Appl.Phys. 2005, 98, 013516. The details of this measurement are included inthe SI.

The nematic texture of the cell without alignment layers (ITO only) withthe NPs printed on one of the surfaces is shown in FIG. 2a . The LC usedhere is MLC-6610 with a negative Δϵ. One can see high qualityhomeotropically aligned features with sharp edges surrounded by aSchlieren texture in the non-printed areas, which is expected of the ITOsurface. It is clear that the absence of NPs on the one of the surfacesdoes not prevent the induction of homeotropic alignment. We neverthelesstested printing NPs on both surfaces. After aligning the two printedfeatures (substrates), high-quality homeotropic alignment was observedin the printed areas, regardless of the LC used.

Printing NPs on a planar polyimide PI-2555 layer leads to thehomogeneous alignment of the LC along the rubbing direction of thepolyimide (FIG. 2b ). One can see traces of the printed NP droplets inthe homogeneous LC texture. In some cases, however, the printed NPdroplets led to the distorted director configuration that showed as thehigh contrast imprint when observed in the polarized light opticalmicroscope (FIG. 2c ). The same effect was also observed for all othertested LCs. Using of another polymer alignment layer such as PVA gavesimilar results (FIG. 2d ).

Assuming that the anchoring of the LC to the polymer alignment layer wasoverwhelming the LC-NP anchoring, we tested the alignment layer with thelower anchoring energy—SiO_(x) evaporated at 30° (FIG. 3). In this case,we were able to obtain excellent contrast, patterned alignment filmswith high-quality homeotropic and homogeneous director configurationsover the entire nematic phase range of each LC tested. We were able toprint any arbitrary patterns (FIGS. 3a, b ), but the best qualitypattern is obtained in the case of printing lines that are alignedacross the movement of the printing head (FIG. 3c ). FIG. 3ddemonstrates the uniformity of the homeotropic alignment in the case ofsome of the larger printed features.

We have previously reported that thiol-capped gold NPs doped into anematic LC matrix or deposited on the LC cell surface induce homeotropicalignment that may change to a homogeneous (planar) configuration underthe action of an applied low-frequency electric field or DC electricfield; effectively making the LC material with a positive dielectricanisotropy act like one with the negative dielectric anisotropy as aresult of the formation of electro-hydrodynamic instabilities(convection rolls), see H. Qi, B. Kinkead, T. Hegmann, Adv. Funct.Mater. 2008, 18, 212, H. Qi, T. Hegmann, ACS Appl. Mater. Interf. 2009,1, 1731. and M. Urbanski, B. Kinkead, H. Qi, T. Hegmann, H.-S. Kitzerow,Nanoscale 2010, 2, 1118.

We demonstrated that the LC cells with the printed NPs display this dualalignment mode as well, if the boundary conditions are chosen correctly.For these experiments, some of the cells were filled with theFelix-2900-03 material (used previously) and driven by a DC electricfield (FIG. 4). We found that the effect depends on the surfacealignment layer underneath the printed NPs as well as on surface of theother substrate.

The cell in FIG. 4a features one substrate coated subsequently with ITO,30° SiO_(x), and printed NPs and a second substrate with ITO and PI-1211(as detailed above), and showed an asymmetrical dielectric response,depending on the polarity of the electric field, and an imperfectparallel director configuration in the “field-on”-state. A negativeDC-field returns the cell into the homeotropic state. Switching thefield off also returns the cell to the homeotropic state. The cell inFIG. 4b is made of two identical substrates (ITO+30° SiO_(x)+printedNPs). This particular configuration sometimes shows an irreversibleswitching effect. After the application of a positive DC-field thehomeotropic-parallel configuration transition occurs, but switching thefield OFF does not return the cell in the initial homeotropic state,which appears to support the involvement of convection rolls(accumulated charges on the NPs) in this process. Printing NPs on bothsurfaces (FIG. 4c and S10) eliminates this irreversibility, and thesecells recover the homeotropic alignment after a positive or negative DCvoltage is applied and turned OFF. Particularly relevant for displayapplications based on the vertical alignment mode (VA mode), the nematicmixture with Δϵ<0 (MLC-6610; Δϵ=−3) can be switched with both an AC (1kHz) or DC applied electric field, and shows no irreversibility (seeFigure S11, SI).

Overall, as noted above it was found that the most important aspect ofthe NP printing process is ink formulation. Material ink-jet printers,i.e. their piezo-based cartridges, are very sensitive to the rheologicalproperties of the ink. If either viscosity or surface tension is out ofthe manufacturer's recommended range, it becomes extremely difficult toprint with acceptable precision.

Another important parameter is the printing substrate. First, wettingbetween substrate and ink defines droplet “pixel” size as well asadhesion characteristics. Second, the anchoring properties of thesurface play a crucial role in obtaining the desired alignment andelectro-optical characteristics of an LC cell in the domains withprinted NPs. A prerequisite condition for successful homeotropicalignment of nematic LCs on printed NPs is a stronger anchoring of theLC to the NPs in comparison to the homogeneous alignment “under-layer”.Using this double-layer alignment method, we have shown that it ispossible to manufacture cells with either homeotropic-hybrid orhomeotropic-homogeneous director modulation. However, in the lattercase, an additional step of substrate alignment is required. With theexample of the NPs printed on the surface of PI-2555, it is clear thatintermediate configurations between homeotropic and homogeneous arepossible as well. Hence, by tuning the LC and the printing surface, itis likely possible to achieve any desired director modulation in a thinnematic LC film (FIG. 5a ).

While the current results clearly demonstrate the possibility to utilizethis method for patterned alignment of nematic LCs, some improvementsare needed for a consistent process that can be applied for large-scalefabrication in industrial settings. Most importantly, the droplet volumeof the printer cartridge limits the resolution of the printed patterns.With existing sub-femtoliter ink-jet printers it should be possible todrastically reduce the pixel size and obtain resolutions comparable tophoto-alignment and photolithography techniques, but in a much simplerand much easier and rapidly re-configurable process. This allowscreating electro-optical devices that can work in the optical range,such as Bragg gratings and Fresnel lenses, among others. The resolutiondemonstrated here limits the applicability of the patterned alignment LCdevices to the longer wavelengths of light, such as IR and beyond.

Also, the obtained samples on SiO_(x) show homogeneous textures with twodistinct domains, which are related to the degeneracy of the hybridalignment in these domains. The 30° SiO_(x), due to the symmetry of theevaporation process gives exactly zero pre-tilt alignment, and theinduced pre-tilt of the rubbed homeotropic alignment layer reduces thenumber of domains but does not eliminate them completely. More carefulchoice of the homeotropic alignment layer and control over thebaking/rubbing process may eliminate these defects completely.

The electro-optical effect of the dual alignment mode proposed inearlier work, where the gold NPs were introduced in the LC bulk oruniformly deposited on surfaces, was reproduced, and may lead toadditional useful applications of patterned LC devices with printed NPpatterns. Advancing this study related to this effect is the subject offuture work.

Already established techniques for defining homeotropic directormodulations in LCs including photo-alignment, see: O. Yaroshchuk, Y.Reznikov, J. Mater. Chem. 2012, 22, 286; for a review summarizing workup to 2000: K. Ichimura, Chem. Rev. 2000, 100, 1847, electrodepatterning, see K. H. Kim, S. K. Kim, SID Digest, 2003, 34, 1208, andion-beam alignment, see (a) P. K. Son, J. H. Park, S. S. Cha, J. C. Kim,T.-H. Yoon, S. J. Rho, B. K. Jeon, J. S. Kim, S. K. Lim, K. H. Kim,Appl. Phys. Lett. 2006, 88, 263512; (b) P. K. Son, S.-W. Choi, Surf.Interf. Analysis 2012, 44, 763, or UVO (ultraviolet/ozone) treatment,see J. B. Kim, C. J. Choi, J. S. Park, S. J. Jo, B. H. Hwang, M. K. Jo,D. Kang, S. J. Lee, Y. S. Kim, H. K. Bail, Adv. Mater. 2008, 20, 3073,can readily be applied to form high-resolution patterns. In contrast,ink-jet printing provides unmatched simplicity, flexibility, and thepossibility to use a wide range of substrates (including flexibleplastic), and requires no spin coating, baking or additional wetprocesses. The ink-jet printing process is easily scalable and allowsprinting large batches of the NP patterned substrates for smallerdevices in one run without complex preparations (FIG. 5b ). Anotherattractive feature is the simplicity of pattern preparation. Only aquick and simple bitmap graphics file needs to be created for printingof the pattern (FIG. 5c ), ranging in size from microns to largerfeatures (see cover suggestion), even entire panels.

In conclusion, we have demonstrated a new technique for obtainingpatterned structures with modulated director configuration in LC thinfilms using ink-jet printing of nanoparticles capped with a protectivelayer of hydrocarbon chain, for example alkylthiol-capped gold NPsfeaturing a unique electro-optic response for Δϵ>0 nematic LCs, see M.Urbanski, B. Kinkead, H. Qi, T. Hegmann, H.-S. Kitzerow, Nanoscale 2010,2, 1118, in the printed patterned domains. The printed patterns are atleast stable over several months, and do not show any deterioration withrespect to the alignment quality or any migration of the NPs into thebulk of the aligned LC film. This approach allows production of low-costelectro-optical LC devices featuring a wide range of substrate materialsincluding flexible, see G. C. Jensen, C. E. Krause, G. A. Sotzing, J. F.Rusling, Phys. Chem. Chem. Phys. 2011, 13, 4888, and uneven substratesdue to the use of a printing jet as a non-contact technique. Theapproach applies to various unique types of nanomaterials (metal,carbon-based as well as magnetic and semiconducting metal chalcogenides,etc.), and builds on very easy design and fabrication processes usedalready in the LCD manufacturing industry for the printing of alignmentlayers. Applications include adaptive LC Fresnel lenses, Braggdiffraction gratings, vertical alignment mode LCDs (with or withoutpatterned pixel design), and flexible LCDs, among others.

EXAMPLES

For the NP synthesis, all reagents were purchased from Sigma Aldrichexcept for hydrogen tetrachloroaurate (Alfa-Aesar). All solvents usedwere of EMD Millipore grade purified by a PureSolv solvent purificationsystem (Innovative Technology Inc). Visible absorption spectra of theNPs in toluene were recorded using a dual cell OLIS14 clarityspectrophotometer. Transmission electron microscopy (TEM) analysis wasperformed with a FEI Tecnai TF20 TEM instrument at an acceleratingvoltage of 200 kV. Samples were prepared by evaporating a drop of dilutetoluene solution of particles onto a carbon-coated copper TEM grid (400mesh) and dried overnight. The ¹H NMR spectra were recorded in CDCl₃ atambient temperature on a Bruker DMX 400 MHz spectrometer and referencedinternally to residual solvent peaks at 7.26 (¹H). A Haake MARSrheometer was used to measure the viscosity of the nano-ink.

For printing, we used the desktop material ink-jet printer FujifilmDimatix DMP-2800 (Santa Clara, Calif.) and the cartridges DMCLCP-11610and DMCLCP-11601. The used NP solution was mildly sonicated in astandard ultrasonic water bath for 1 minute before filling the printercartridge. The cartridge was filled with the nano-ink according to themanufacturer's instructions. The cartridge was cleaned before theprinting using the standard cleaning cycle (“Spit-Purge-Blot”).Occasionally, even initially well-dispersed NPs show some tendency foraggregation and clogging of the printing nozzles (i.e. the NP dry out inthe nozzle, where the solvent evaporated). In such case, if thecartridge was not used for a prolonged period of time (usually severaldays), de-clogging by heating to 50° C. and running the cleaning cycleseveral times solved this issue. We found that the lifetime of a filledcartridge is at least 6 months after initial filling, after which timeit becomes more difficult to de-clog. Jetting of the ink out of thenozzles is controlled by a “jetting waveform” that defines theapplication of voltage to the piezo-elements inside the cartridge, seeFIG. 10 for a desirable waveform.

Focused ion beam assisted scanning electron microscopy (FIB-SEM) wasperformed on a PEI-Helios Nanolab 650 instrument at an acceleratingvoltage of 2 kV to measure the printed NP film/feature thickness. Forthese measurements, two layers of the NPs were printed right on top ofone another on a pre-cleaned glass substrate (without ITO or analignment layer), realized by the precise positioning of the substratefeature of the materials printer. The solvent was evaporated and thesubstrate was vacuum-dried at 35-40° C. The sample for FIB-SEM wasprepared by coating the dried printed film on a glass substrate with aprotective layer of palladium and platinum to protect the sampleunderneath from damage during the gallium ion milling employed to exposea cross-section of the printed sample area.

For the preparation of substrates for printing, a homogeneous alignmentlayer of SiO_(x) evaporated at 30° was deposited using the vacuumthermal evaporation system produced by Kurt J. Lesker Company (JeffersonHills, Pa.). Homogeneous alignment materials PI-2555 and polyvinylalcohol (PVA) were purchased from HD Microsystems and Sigma Aldrich,respectively. The homeotropic alignment material SE-1211 was purchasedfrom Nissan Chemicals. ITO-covered glass substrates were purchased fromColorado Concept Coating (Loveland, Colo.).

For the cell assembly, UV-sensitive adhesive Norland 68 and 5 μm silicaspheres spacers from Nippon were used. A vacuum LC cell filling stationfrom LC Technologies was used for the filling of the cells.

The liquid crystals used in the experiments were5-n-heptyl-2-(4-n-octyloxy-phenyl)pyrimidine (Felix-2900-03) fromSynthon Chemicals, 4-cyano-4′-pentylbiphenyl (5CB) from TCI, thepositive Δϵ mixture TL203, and the negative Δϵ mixture MLC-6610 bothfrom Merck (see Table S1, SI).

Assembled and filled LC cells were observed using a polarized lightoptical microscope (Olympus BX-53). The azimuthal axis of the liquidcrystal director was approximately at 45° with respect to the axis ofthe crossed polarizer and analyzer. The temperature of the cell wascontrolled by a hot stage (Linkam LTS420E). A function generator card(National Instruments PCI-5402) was used to drive the cells forelectro-optics observations. A digital oscilloscope (Agilent DSOX2012A)was used to control the driving waveform.

All glassware used for preparation and storage of nanoparticles (NPs)and nano-ink was treated with aqua regia, rinsed with deionized (DI)water (Millipore, resistivity 18.2 MΩ) and acetone, and then dried at120° C. Gold NPs capped with dodecanethiol were synthesized using thetwo-phase Brust-Schiffrin method, see M. Brust, M. Walker, D. Bethell,D. J. Schiffrin, R. Whyman, J. Chem. Soc., Chem. Comm. 1994, 801.Briefly, tetraoctylammonium bromide (347 mg, 0.63 mmol) was dissolved indry toluene (25 mL) and was added to HAuCl₄•3H₂O (100 mg, 0.25 mmol)dissolved in DI water (10 mL). The mixture was allowed to vigorouslystir for 15 minutes to ensure complete transfer of AuCl₄ ⁻ into thetoluene phase (color changes to orange). Dodecanethiol (0.97 mL, 4.06mmol) was added, and the color immediately changed from orange togrey-white. Then, sodium borohydride (19 mg, 0.507 mmol), dissolved inDI water (1 mL), was added over a time period of 30 seconds. The colorof the organic layer changed to reddish-brown. The reaction mixture wasallowed to stir for three hours. Thereafter, the aqueous layer wasremoved and the organic layer evaporated under vacuum at 70 mbar(keeping the temperature below 45° C.). The NPs were then precipitatedby adding 250 mL of ethanol, and this solution was kept at 4° C. forfour hours. The precipitate formed was collected by centrifugation. There-dispersion and precipitation process was repeated twice. Finally,particles were washed with methanol and acetone followed by DI water.The obtained black precipitate was then dissolved in chloroform, thesolvent removed under vacuum, and the particles dried under dry nitrogen(covering the flask with aluminum foil). The purified NPs werecharacterized by ¹H NMR spectroscopy, UV-vis spectrophotometry, andHR-TEM analysis/imaging. The obtained gold NPs were stable and did notshow signs of decomposition over a period of several months. The NPssize determined by TEM image analysis was determined to 1.9±0.4 nm. Thesynthesized gold NPs did not show a weak surface plasmon resonance peak,which further supported that particles are smaller than 5 nm, see A.Henglein, D. Meisel, Langmuir 1998, 14, 7392., and A. Henglein, Langmuir1998, 14, 6738.

The polar anchoring energy was measured in the following experimentfollowing the method described in X. Nie, Y. H. Lin, T. X. Wu, H. Wang,Z. Ge, S. T. Wu, J. Appl. Phys. 2005, 98, 013516. A vertical alignment(VA) liquid crystal cell with the cell gap of 4.8 μm was made with theNPs printed on both surfaces (ITO-covered glass substrates). The cellwas filled with the liquid crystal mixture MLC6610 with negativedielectric anisotropy (Δϵ=−3.1). The cell was placed between crossedpolarizers with the azimuthal projection of the director at the 45°angle to the polarizers' transmission axis. Optical transmission of thesystem as a function of applied AC-voltage (f=10 kHz) was measured. Thiscurve was used to calculate the cell's phase retardation R as a functionof applied voltage V, the values of threshold voltage, and the maximumphase retardation of the cell R₀. We used the theoretical value of thecell capacitance instead of experimental one, which slightly decreases(usually within 5%) the accuracy of the measurement, but makes theexperiment much simpler. The anchoring energy value was calculated usingthe fitting slope method from the normalized phase retardation as thefunction of the reduced voltage V-V′ (see FIG. 13).

While in accordance with the patent statutes the best mode and preferredembodiment have been set forth, the scope of the invention is notlimited thereto, but rather by the scope of the attached claims.

What is claimed is:
 1. A method for forming a liquid crystal cell,comprising the steps of: obtaining a liquid cell substrate, wherein anelectrode layer is present on a surface of the substrate, wherein analignment layer is optionally present on the electrode layer; obtaininga capped nanoparticle-containing composition comprising a) ananoparticle capped with a protective layer of hydrocarbon chains and b)a solvent; wherein said protective layer of hydrocarbon chains comprisea chiral group bonded by a linkage compound to said nanoparticle,wherein said linkage compound comprises a thiol linkage, a bis-thiollinkage, a thiosulfate linkage, a phosphorus linkage, a silane linkage,a siloxane linkage, or a carboxylate linkage; and printing a first layerof the composition on one or more portions of a cell surface with anink-jet printer.
 2. The method according to claim 1, wherein the solventis o-xylene.
 3. The method according to claim 1, wherein the cappednanoparticle-containing composition is printed on one or more portionsof one or more of the electrode layer and/or the alignment layer.
 4. Themethod according to claim 3, wherein the capped nanoparticle-containingcomposition is printed on two or more portions of the one or more of theelectrode layer and/or the alignment layer with the printing beingderived from droplets of said nanoparticles.
 5. The method according toclaim 1, wherein a second layer of the capped nanoparticle-containingcomposition is overprinted on the first layer.
 6. The method accordingto claim 5, wherein an additional layer of the cappednanoparticle-containing composition is overprinted on the second layer.7. The method according to claim 3, wherein the substrate is flexible.8. The method according to claim 3, further including the step ofplacing a liquid crystal material in contact with at least a portion ofthe printed first layer.
 9. The method according to claim 1, furtherincluding the step of obtaining a second composition comprising adifferent nanoparticle capped with a protective layer of hydrocarbonchains and a solvent, and simultaneously printing a first layer of thesecond composition on one or more portions of the cell surface with anink-jet printer during printing of the first layer of the composition.10. The method according to claim 9, further printing a second layer ofthe second composition on one or more of the first layer of thecomposition and the first layer of the second composition.
 11. Themethod according to claim 1, wherein the capped nanoparticle-containingcomposition is printed at a resolution of greater than 500 dpi.
 12. Themethod according to claim 1, wherein the printing step results in a cellhaving a patterned dual electro-optic mode.
 13. The method according toclaim 3, wherein the alignment layer is present and is located beneathat least one portion of the capped nanoparticle-containing composition,wherein the cell has a pretilt that is planar, tilted, or homeotropic.14. The method according to claim 1, wherein the printing results in thelayer having a feature (size of the printed droplets) of around 30micron in diameter or smaller depending on the piezo nozzle used. 15.The method according to claim 3, further including the step of forming acell including a pair of substrates, wherein a separate electrode layeris present on a surface of each substrate, wherein an alignment layer ispresent on each electrode layer, and wherein the cappednanoparticle-containing composition is printed in the form of a patternon one or more portions of the alignment layer on at least one of thesubstrates.
 16. The method according to claim 1, wherein the particlesize of said capped nanoparticle is from 1 to 10 nm.
 17. The methodaccording to claim 1, wherein the particle size of said cappednanoparticle is from 1 to 5 nm.
 18. The method according to claim 3,wherein the particle size of said capped nanoparticle is from 1 to 10nm.
 19. The method according to claim 9, wherein the particle size ofsaid capped nanoparticle is from 1 to 5 nm.
 20. The method according toclaim 13, wherein the particle size of said capped nanoparticle is from1 to 5 nm.